SuperWASP observations of long timescale photometric variations in cataclysmic variables

Aims: We investigated whether the predictions and results of Stanishev et al. (2002, A&A, 394, 625) concerning a possible relationship between eclipse depths in PX And and its retrograde disc precession phase, could be confirmed in long term observations made by SuperWASP. In addition, two further CVs (DQ Her and V795 Her) in the same SuperWASP data set were investigated to see whether evidence of superhump periods and disc precession periods were present and what other, if any, long term periods could be detected. Methods: Long term photometry of PX And, V795 Her and DQ Her was carried out and Lomb-Scargle periodogram analysis undertaken on the resulting light curves. For the two eclipsing CVs, PX And and DQ Her, we analysed the potential variations in the depth of the eclipse with cycle number. Results: The results of our period and eclipse analysis on PX And confirm that the negative superhump period is 0.1417 ± 0.0001d. We find no evidence of positive superhumps in our data suggesting that PX And may have been in a low state during our observations. We improve on existing estimates of the disc precession period and find it to be 4.43 ± 0.05d. Our results confirm the predictions of Stanishev et al. (2002). We find that DQ Her does not appear to show a similar variation for we find no evidence of negative superhumps or of a retrograde disc precession. We also find no evidence of positive superhumps or of a prograde disc precession and we attribute the lack of positive superhumps in DQ Her to be due to the high mass ratio of this CV. We do however find evidence for a modulation of the eclipse depth over a period of 100 days which may be linked with solar-type magnetic cycles which give rise to long term photometric variations. The periodogram analysis for V795 Her detected the likely positive superhump period 0.1165d, however, neither the 0.10826d orbital period nor the prograde 1.53d disc precession period were seen. Here though we have found a variation in the periodogram power function at the positive superhump period, over a period of at least 120 days.

WASP-8b: a retrograde transiting planet in a multiple system

We report the discovery of WASP-8b, a transiting planet of 2.25 ± 0.08 MJup on a strongly inclined eccentric 8.15-day orbit, moving in a retrograde direction to the rotation of its late-G host star. Evidence is found that the star is in a multiple stellar system with two other companions. The dynamical complexity of the system indicates that it may have experienced secular interactions such as the Kozai mechanism or a formation that differs from the “classical” disc-migration theory.

The spin-orbit alignment of the transiting exoplanet WASP-3b from Rossiter-McLaughlin observations

We present an observation of the Rossiter-McLaughlin effect for the planetary system WASP-3. Radial velocity measurements were made during transit using the SOPHIE spectrograph at the 1.93-m telescope at Haute-Provence Observatory. The shape of the effect shows that the sky-projected angle between the stellar rotation axis and planetary orbital axis (?) is small and consistent with zero within . WASP-3b joins the ~two-thirds of planets with measured spin-orbit angles that are well aligned and are thought to have undergone a dynamically gentle migration process such as planet-disc interactions. We find a systematic effect which leads to an anomalously high determination of the projected stellar rotational velocity (vsini = 19.6+2.2-2.1kms-1) compared to the value found from spectroscopic line broadening (vsini = 13.4 +/- 1.5kms-1). This is thought to be caused by a discrepancy in the assumptions made in the extraction and modelling of the data. Using a model developed by Hirano et al. designed to address this issue, we find vsini to be consistent with the value obtained from spectroscopic broadening measurements (vsini = 15.7+1.4-1.3kms-1).

An ingress and a complete transit of HD80606 b

We have used four telescopes at different longitudes to obtain near-continuous light-curve coverage of the star HD80606 as it was transited by its ~4-MJup planet. The observations were performed during the predicted transit windows around 2008 October 25 and 2009 February 14. Our data set is unique in that it simultaneously constrains the duration of the transit and the planet's period. Our Markov Chain Monte Carlo analysis of the light curves, combined with constraints from radial-velocity data, yields system parameters consistent with previously reported values. We find a planet-to-star radius ratio marginally smaller than previously reported, corresponding to a planet radius of Rp = 0.921 +/- 0.036RJup.

Dust and the Type II-Plateau Supernova 2004et

We present mid-infrared (MIR) observations of the Type II-plateau supernova (SN) 2004et, obtained with the Spitzer Space Telescope between 64 and 1406 days past explosion. Late-time optical spectra are also presented. For the period 300-795 days past explosion, we argue that the spectral energy distribution (SED) of SN 2004et comprises (1) a hot component due to emission from optically thick gas, as well as free-bound radiation; (2) a warm component due to newly formed, radioactively heated dust in the ejecta; and (3) a cold component due to an IR echo from the interstellar-medium dust of the host galaxy, NGC 6946. There may also have been a small contribution to the IR SED due to free-free emission from ionized gas in the ejecta. We reveal the first-ever spectroscopic evidence for silicate dust formed in the ejecta of a supernova. This is supported by our detection of a large, but progressively declining, mass of SiO. However, we conclude that the mass of directly detected ejecta dust grew to no more than a few times 10(-4) M-circle dot. We also provide evidence that the ejecta dust formed in comoving clumps of fixed size. We argue that, after about two years past explosion, the appearance of wide, box-shaped optical line profiles was due to the impact of the ejecta on the progenitor circumstellar medium and that the subsequent formation of a cool, dense shell was responsible for a later rise in the MIR flux. This study demonstrates the rich, multifaceted ways in which a typical core-collapse supernova and its progenitor can produce and/or interact with dust grains. The work presented here adds to the growing number of studies that do not support the contention that SNe are responsible for the large mass of observed dust in high-redshift galaxies.

Extensive optical and near-infrared observations of the nearby, narrow-lined type Ic SN 2007gr: days 5 to 415

We present photometric and spectroscopic observations at optical and near-infrared wavelengths of the nearby type Ic supernova 2007gr. These represent the most extensive data-set to date of any supernova of this sub-type, with frequent coverage from shortly after discovery to more than one year post-explosion. We deduce a rise time to B-band maximum of 11.5 +/- 2.7 d. We find a peak B-band magnitude of M-B = -16.8, and light curves which are remarkably similar to the so-called "hypernova" SN 2002ap. In contrast, the spectra of SNe 2007gr and 2002ap show marked differences, not least in their respective expansion velocities. We attribute these differences primarily to the density profiles of their progenitor stars at the time of explosion i.e. a more compact star for SN 2007gr compared to SN 2002ap. From the quasi-bolometric light curve of SN 2007gr, we estimate that 0.076 +/- 0.010 M-circle dot of Ni-56 was produced in the explosion. Our near-infrared (IR) spectra clearly show the onset and disappearance of the first overtone of carbon monoxide (CO) between similar to 70 to 175 d relative to B-band maximum. The detection of the CO molecule implies that ionised He was not microscopically mixed within the carbon/oxygen layers. From the optical spectra, near-IR light curves, and colour evolution, we find no evidence for dust condensation in the ejecta out to about +400 d. Given the combination of unprecedented temporal coverage, and high signal-to-noise data, we suggest that SN 2007gr could be used as a template object for supernovae of this sub-class.

Turning Asteroids into Comets with ELTs

It is clear that ELTs will be able to detect extremely weak outgassing from Solar system bodies via a number of different methods. Occultations will allow probing for outgassing around 20 km main-belt asteroids. Imaging can reveal dust emission rates of only milligrams/second in the inner solar system, while sublimation rates of gasses should be measurable down to gram/second levels. Suitable targets will be identified via the coming all-sky surveys, through both the classical dynamical Tisserand Invariant and long-baseline lightcurves. It is possible that using these methods, ELTs may allow the discovery of much more activity throughout the Solar system than is presently known.

Shock creation and particle acceleration driven by plasma expansion into a rarefied medium

The expansion of a dense plasma through a more rarefied ionized medium is a phenomenon of interest in various physics environments ranging from astrophysics to high energy density laser-matter laboratory experiments. Here this situation is modeled via a one-dimensional particle-in-cell simulation; a jump in the plasma density of a factor of 100 is introduced in the middle of an otherwise equally dense electron-proton plasma with an uniform proton and electron temperature of 10 eV and 1 keV, respectively. The diffusion of the dense plasma, through the rarefied one, triggers the onset of different nonlinear phenomena such as a strong ion-acoustic shock wave and a rarefaction wave. Secondary structures are detected, some of which are driven by a drift instability of the rarefaction wave. Efficient proton acceleration occurs ahead of the shock, bringing the maximum proton velocity up to 60 times the initial ion thermal speed. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3469762]

The Doppler shadow of WASP-3b. A tomographic analysis of Rossiter-McLaughlin observations

Context. Hot-Jupiter planets must form at large separations from their host stars where the temperatures are cool enough for their cores to condense. They then migrate inwards to their current observed orbital separations. Different theories of how this migration occurs lead to varying distributions of orbital eccentricity and the alignment between the rotation axis of the star and the orbital axis of the planet. Aims: The spin-orbit alignment of a transiting system is revealed via the Rossiter-McLaughlin effect, which is the anomaly present in the radial velocity measurements of the rotating star during transit due to the planet blocking some of the starlight. In this paper we aim to measure the spin-orbit alignment of the WASP-3 system via a new way of analysing the Rossiter-McLaughlin observations. Methods: We apply a new tomographic method for analysing the time variable asymmetry of stellar line profiles caused by the Rossiter-McLaughlin effect. This new method eliminates the systematic error inherent in previous methods used to analyse the effect. Results: We find a value for the projected stellar spin rate of v sin i = 13.9 ± 0.03 km s-1 which is in agreement with previous measurements but has a much higher precision. The system is found to be well aligned, with ? = 5-5+6° which favours an evolutionary history for WASP-3b involving migration through tidal interactions with a protoplanetary disc. From comparison with isochrones we put an upper limit on the age of the star of 2 Gyr.

WASP-29b: A Saturn-sized Transiting Exoplanet

We report the discovery of a Saturn-sized planet transiting a V = 11.3, K4 dwarf star every 3.9 days. WASP-29b has a mass of 0.24 ± 0.02 M Jup and a radius of 0.79 ± 0.05 R Jup, making it the smallest planet so far discovered by the WASP survey, and the exoplanet most similar in mass and radius to Saturn. The host star WASP-29 has an above-solar metallicity and fits a possible correlation for Saturn-mass planets such that planets with higher-metallicity host stars have higher core masses and thus smaller radii.

WASP-22 b: A Transiting "Hot Jupiter" Planet in a Hierarchical Triple System

We report the discovery of a transiting planet orbiting the star TYC 6446-326-1. The star, WASP-22, is a moderately bright (V = 12.0) solar-type star (Teff = 6000 ± 100 K, [Fe/H] = -0.05 ± 0.08). The light curve of the star obtained with the WASP-South instrument shows periodic transit-like features with a depth of about 1% and a duration of 0.14 days. The presence of a transit-like feature in the light curve is confirmed using z-band photometry obtained with Faulkes Telescope South. High-resolution spectroscopy obtained with the CORALIE and HARPS spectrographs confirms the presence of a planetary mass companion with an orbital period of 3.533 days in a near-circular orbit. From a combined analysis of the spectroscopic and photometric data assuming that the star is a typical main-sequence star we estimate that the planet has a mass M p = 0.56 ± 0.02M Jup and a radius R p = 1.12 ± 0.04R Jup. In addition, there is a linear trend of 40 m s-1 yr-1 in the radial velocities measured over 16 months, from which we infer the presence of a third body with a long-period orbit in this system. The companion may be a low mass M-dwarf, a white dwarf, or a second planet.

Orbital period variations of hot Jupiters caused by the Applegate effect

Several authors have shown that precise measurements of transit time variations of exoplanets can be sensitive to other planetary bodies, such as exo-moons. In addition, the transit timing variations of the exoplanets closest to their host stars can provide tests of tidal dissipation theory. These studies, however, have not considered the effect of the host star. There is a large body of observational evidence that eclipse times of binary stars can vary dramatically due to variations in the quadrupole moment of the stars driven by stellar activity. In this paper, we investigate and estimate the likely impact such variations have on the transit times of exoplanets. We find in several cases that such variations should be detectable. In particular, the estimated period changes for WASP-18b are of the same order as those expected for tidal dissipation, even for relatively low values of the tidal dissipation parameter. The transit time variations caused by the Applegate mechanism are also of the correct magnitude and occur on time-scales such that they may be confused with variations caused by light-travel time effects due to the presence of a Jupiter-like second planet. Finally, we suggest that transiting exoplanet systems may provide a clean route (compared to binaries) to constraining the type of dynamo operating in the host star.

Rotation periods of exoplanet host stars

The stellar rotation periods of 10 exoplanet host stars have been determined using newly analysed CaII H&K flux records from the Mount Wilson Observatory and Strömgren b, y photometric measurements from Tennessee State University's automatic photometric telescopes at the Fairborn Observatory. Five of the rotation periods have not previously been reported, with that of HD 130322 very strongly detected at Prot = 26.1 +/- 3.5 d. The rotation periods of five other stars have been updated using new data. We use the rotation periods to derive the line-of-sight inclinations of the stellar rotation axes, which may be used to probe theories of planet formation and evolution when combined with the planetary orbital inclination found from other methods. Finally, we estimate the masses of 14 exoplanets under the assumption that the stellar rotation axis is aligned with the orbital axis. We calculate the mass of HD 92788 b (28 MJ) to be within the low-mass brown dwarf regime and suggest that this object warrants further investigation to confirm its true nature.

Dust and the type II-Plateau supernova 2004dj

We present mid-infrared (MIR) spectroscopy of a Type II-plateau supernova, SN 2004dj, obtained with the Spitzer Space Telescope, spanning 106--1393d after explosion. MIR photometry plus optical/near-IR observations are also reported. An early-time MIR excess is attributed to emission from non-silicate dust formed within a cool dense shell (CDS). Most of the CDS dust condensed between 50d and 165d, reaching a mass of $0.3x^(-5)Msun. Throughout the observations much of the longer wavelength (>10microns) part of the continuum is explained as an IR echo from interstellar dust. The MIR excess strengthened at later times. We show that this was due to thermal emission from warm, non-silicate dust formed in the ejecta. Using optical/near-IR line-profiles and the MIR continua, we show that the dust was distributed as a disk whose radius appeared to be slowly shrinking. The disk radius may correspond to a grain destruction zone caused by a reverse shock which also heated the dust. The dust-disk lay nearly face-on, had high opacities in the optical/near-IR regions, but remained optically thin in the MIR over much of the period studied. Assuming a uniform dust density, the ejecta dust mass by 996d was 0.5+/-0.1 x 10^(-4)Msun, and exceeded 10^(-4)Msun by 1393d. For a dust density rising toward the center the limit is higher. Nevertheless, this study suggests that the amount of freshly-synthesized dust in the SN 2004dj ejecta is consistent with that found from previous studies, and adds further weight to the claim that such events could not have been major contributors to the cosmic dust budget.

Chemical evolution of protoplanetary disks - the effects of viscous accretion, turbulent mixing and disk winds

We calculate the chemical evolution of protoplanetary disks considering radial viscous accretion, vertical turbulent mixing, and vertical disk winds. We study the effects on the disk chemical structure when different models for the formation of molecular hydrogen on dust grains are adopted. Our gas-phase chemistry is extracted from the UMIST Database for Astrochemistry (Rate06) to which we have added detailed gas-grain interactions. We use our chemical model results to generate synthetic near- and mid-infrared local thermodynamic equilibrium line emission spectra and compare these with recent Spitzer observations. Our results show that if H2 formation on warm grains is taken into consideration, the H2O and OH abundances in the disk surface increase significantly. We find that the radial accretion flow strongly influences the molecular abundances, with those in the cold midplane layers particularly affected. On the other hand, we show that diffusive turbulent mixing affects the disk chemistry in the warm molecular layers, influencing the line emission from the disk and subsequently improving agreement with observations. We find that NH3, CH3OH, C2H2, and sulfur-containing species are greatly enhanced by the inclusion of turbulent mixing. We demonstrate that disk winds potentially affect the disk chemistry and the resulting molecular line emission in a manner similar to that found when mixing is included.